The invention relates generally to foam-in-place packaging systems, and in particular to foam packaging products that are prepared from mixing foam precursors together to form a foam.
Foam-in-place packaging is a technique for producing cushioning that is used in the packaging of fragile articles to be shipped. Foam-in-place packaging comprises generating foam cushioning on an as-needed basis while the article to be protected is being packaged. In general, foam-in-place packaging employs foamable compositions that are produced by mixing two or more precursor chemicals that react to form a polymer foam that hardens on curing. For example, a liquid polyol-containing precursor and a liquid isocyanate-containing precursor may be mixed and reacted to form a polyurethane foam. The resulting foam occupies a volume that is many times the volume of the liquid precursors.
One technique for foam-in place packaging is to place the article to be packaged in a container, and then to place one or more flexible plastic bags containing a foamable composition into the container. The foamable composition expands to cause the bag to fill the void spaces between the walls of the container and the article, and then hardens. The result is a foam cushion that conforms closely to the shape of the article and the container, and thereby protects the article. The bags prevent the expanding foam from contacting the walls of the container and the article. The foam cushion is sometimes referred to as a “foam-in-bag” cushion or package.
The packaging requirements of various users may often differ and typically no one packaging system can meet the needs of every potential user. As a result, many different techniques for preparing and using foam-in-place packaging systems have been developed.
A number of automated devices have been developed for rapidly making a relatively large number of bags for foam-in-bag packaging, and are assigned to the assignee of the present application. Exemplary devices are described and claimed in U.S. Pat. Nos. 4,674,268; 4,800,708; 4,854,109; 5,376,219; and 6,003,288. The resulting bags should be placed in the containers immediately after the precursors are dispensed and mixed because the precursors react quickly to form the foam. These devices are particularly suitable for use in situations where it is desirable and feasible to fill the bags with foam precursors at the location where articles are being packaged. Certain systems of this type are sometimes referred to as two-component systems because a polyurethane foam is typically prepared by reacting a polyol component with an isocyantate component.
It may not always be desirable or feasible to have an extensive system for preparing the bags or injecting foam precursors into a bag. In such cases, the user may require a foam-in-bag cushion that has the precursors pre-disposed in separate compartments in the bag. When desired, the user can combine the precursors in the bag to form the foam cushion. Exemplary devices are described and claimed in U.S. Pat. Nos. 5,699,902, 5,899,325, and 5,996,782.
The foam that is used in a foam-in-bag package may be a high or low density foam. Higher density foam is often used because of its ability to protect articles from a greater amount of shock and accommodate higher static loads. Generally, higher density foam tends to produce more heat from the reaction of the foam precursors during the foam formation process. Typically, the higher the density of the foam, the greater amount of heat that is produced during foam formation, although this is not necessarily so.
During the foam formation reaction, the temperature within the foam core can reach and exceed the melting temperature of the bag's thermoplastic material. If two or more foam cushions are in contact, the surface temperature of the adjoining cushions can often reach temperatures that will fuse the adjoining bags to one another. As a result, the cushions can be difficult to separate, and the article could be damaged during cushion separation. To prevent the cushions from fusing together, the cushions can be separated until they have sufficiently cooled off. Separating the cushions can create inefficiencies in the packaging system and make it more difficult to achieve packaging that conforms to the shape of the article.
Special high-temperature films can also be used to prevent the film layer from fusing to the film on the adjoining cushion. Generally these films are composed of at least two layers with an inner layer of high density polyethylene, or similar polymer, and the outer layer composed of a high-melting point polymer such as polyamide, polyester or polymethyl pentene. The two layers can be co-extruded, extrusion coated or laminated together. A third layer, called a tie layer is typically included between the two layers to allow otherwise incompatible resins to adhere.
These composite high-temperature films tend to be expensive and difficult to fabricate. They also tend to be stiff and crinkly, and have high tear propagation. In addition, they can be difficult to use in foam-in-bag machines because they cannot be readily cut with a hot cross cut wire on existing equipment.